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Comparison: Human Body, Safe Nutrient Intakes and Leaky Buckets

By Michael McBurney

The 3rd International Vitamin Conference ended yesterday in Washington DC. Staff from the NIH National Institute of Standards and Technology (NIST) and Office of Dietary Supplements (ODS) were actively involved in the conference. Presentations and discussions often centered on the importance of standards and robust, validated methods to accurately measure vitamins in products (e.g. foods and supplements) and biological matrices (e.g. blood, urine, biopsies). Commutability was a frequently used term. Why? Because the merging of data acquired at many laboratories using different equipment at any time requires an understanding of the equivalence of numbers derived using different analytical procedures.

It is important to know if +49% to -28% shifts in serum 25(OH)D3 concentrations reflect seasonal variation subcutaneous vitamin D synthesis from sun exposure (Cashman et al, 2014) or might be attributable to laboratory assay drift. Without robust laboratory methods and evidence that intra- and inter-assay variability is constrained, one could incorrectly conclude that vitamin levels (in something - product, blood, etc) are trending when the issue is analytical migration.

At many times during the conference, experts discussed safety concerns of excessive nutrient intakes. Because many vitamins are sensitive to oxidation and moisture, federal mandates (CFR 101.9) depend upon vitamin overages at time of manufacture to ensure labeled vitamin levels per serving at time of consumption. Overages are usually determined based on shelf life expectations and rate of disappearance.

People can harm themselves from repeated bad choices. Too little or too much nutrition is never optimal. For example, the health of a child may be affected for a lifetime if placental transfer of vitamin D is compromised during pregnancy. And despite high levels of sunshine in the Mediterranean regions, maternal hypovitaminosis D during pregnancy remains common. What is the safest remedy? Should foods be fortified with vitamin D? Should vitamin D supplementation be recommended? How often should a vitamin D supplement be taken? What concentration? What about vitamin A? Vitamin C? Folate? At IVC14, experts discussed the pros and cons of fortification, biofortification and dietary supplementation.

Our bodies are like a bucket with a hole in the bottom. Optimal nutritional status can be conceptualized as keeping a leaky bucket full, or nearly full with water (nutrients). When the bucket is almost empty or the hole in the bottom is large, water (nutrients) have to be added at a rate to overcome the loss and faster if the goal is to fill the empty void. There is little concern about adding water (nutrients) too fast until the bucket is nearly full. Like a bucket, a safe nutrient intake is a function of pool size (bucket), rate of consumption (intake), and metabolism (leakiness).